The genome of the typical retrovirus encodes three primary enzymes that mediate the virus replication cycle. Reverse transcriptase converts the viral RNA genome into a double stranded DNA. Integrase nonspecifically inserts this DNA copy into the host cell genome, and protease cleaves viral structural and nonstructural proteins into their mature forms.
An essential step of the retroviral life cycle is the integration of its double-stranded DNA copy into the host genome. H. Sakai et al, J. Virol. 67:1169 (1993). This process requires highly conserved sequence recognition and cleaving steps. For this reason, a therapeutic agent that can interrupt this process should be an effective and specific antiviral agent. A protein at the C-terminus of the viral polymerase, integrase (IN), is the only viral protein required for this process. R. LaFemina et al., J. Virol. 66:7414 (1992).
A. Fesen et al., Proc. Natl. Acad. Sci. USA 90:2399 (1993) discuss investigations using an in vitro integrase assay of a variety of chemicals as potential human immunodeficiency virus type I (HIV-1) integrase inhibitors. The article reports several topoisomerase inhibitors, such as doxorubicin, mitoxantrose, ellipticines and quercetin as potent inhibitors. While some topoisomerase inhibitors were excellent anti-integrase agents, no correlation was observed with antiviral effects. This is believed to be at least partially due to the fact that a number of topoisomerase inhibitors have severe cytotoxic effects, depending upon their mechansim of inhibition.
R. LaFemina et al., J. Virology 56:7414 (1992) reports studies assessing the usefulness of the integrase enzyme as a target for specific HIV-1 anti-viral therapeutic agents by determining its absolute requirement for productive HIV-1 infection. The article reports the results of the introduction of specific amino acid substitution into recombinant integrase and assesses the ability of the mutant proteins to properly mediate specific and non-specific cleavage as well as integration.